1. Field of the Invention
This invention relates to substrates on which epitaxial single crystal layers, e.g., of materials such as diamond, cubic boron nitride, cubic boron phosphide, beta-silicon carbide, gallium nitride, and the like, may be deposited, and also relates to the substrate articles comprising such substrates and the epitaxial single crystal layers deposited thereon, as well as to semiconductor devices manufactured from such substrate articles. The invention further relates to a surface texturing method for making such substrates, and to methods of making the related epitaxial single crystal substrate articles, and the related semiconductor devices.
2. Description of the Related Art
In the field of semiconductor devices, crystalline materials such as diamond, cubic boron nitride, cubic boron phosphide, beta-silicon carbide, gallium nitride, and the like have been viewed as potentially desirable materials for forming epitaxial substrate layers for semiconductor manufacture, due to their advantageous physical and electronic properties, amenability to doping, etc.
Diamond in particular has been regarded as a potentially highly useful material for such applications. Accordingly, the ensuing background discussion of the present invention will be directed to diamond, however it will be appreciated that similar considerations apply to other crystalline materials such as those illustratively referred to above in the preceding paragraph.
One of the primary problems facing diamond semiconductor device fabrication is the inability to form large area, high quality single crystal diamond films.
Unfortunately, however, the state of the art in diamond film formation has not matured to a point where large area, defect-free single crystal thin films can be produced.
At the present time, large area diamond films formed by known growth techniques are polycrystalline in character. This fact has greatly restricted the application of diamond in the fabrication of high performance semiconductor devices.
The reasons for the inability of conventional technology to form large area single crystal diamond films is not fully understood, but is partially attributable to the fact that the diamond surface has a high specific surface energy. As an example, the diamond (111) surface energy is approximately 3760 ergs per square centimeter, whereas for a corresponding (111) surface of silicon, the surface energy is on the order of only about 1250 ergs per square centimeter. As a result, the high surface energy values associated with diamond favor the formation of three-dimentional nuclei during the initial stages of diamond film formation by vapor phase techniques, e.g., the hot tungsten-filament method disclosed by S. Matsumoto, et al, Japanese Journal of Applied Physics, Vol. 21, L183 (1982), as well as other chemical vapor deposition techniques. These three-dimensional nuclei in turn cause the formation of polycrystalline diamond films when diamond is grown on substrate materials having a much lower surface energy than diamond itself.
In the early stages of growth of diamond films by vapor deposition techniques, before a continuous polycrystalline film is formed, isolated islands of diamonds initially appear on the substrate surface. Such islands are of single crystal character, with sizes varying widely but typically on the order of 2-10 micrometers on a side.
At this initial stage of diamond film formation, it is possible to grow high quality single crystals of diamond, however these tiny diamond islands are randomly scattered on the substrate, rendering it impossible to effectively utilize them for semiconductor device fabrication purposes. In addition, such diamond islands are not oriented with respect to the substrate surface, i.e., they exhibit no preferred orientation.
Subsequently, as film growth proceeds beyond the initial stage which is characterized by scattered islands of single crystal diamond, additional nucleation occurs on the faces of the small crystalite regions, and polycrystalline films are formed.
Another problem faced by attempts to grow high quality single crystals of diamond for semiconductor manufacturing application is the paucity of suitable substrate materials having the proper surface geometry and suitably close lattice matching of the substrate with the diamond lattice (i.e., having a lattice constant within about 10% of the diamond lattice constant). Nickel and copper are among the closest lattice matched materials to diamond, however despite their close lattice matching characteristics, these substrate materials either have surface energies which are lower than the diamond surface energy and/or they exhibit a large solubility for carbon and thus are unsuitable for diamond film formation methods utilizing vapor-phase carbonaceous precursors such as methane. As a result, single crystalline diamond films have not been grown on these substrate materials.
Insulating single crystals of bulk diamond are known, and can be readily manufactured by conventional techniques, as well as being of naturally occurring origin. Such diamond obviously represents a favorable substrate composition for growth of high quality epitaxial single crystals of semiconducting diamond, since the surface energies of the substrate material and the desired single crystal semiconducting diamond are identical or nearly identical, and the lattice constants of the insulating diamond and the semiconducting diamond are substantially equal.
Despite the favorable surface energies and lattice constants of epitaxial diamond and bulk single crystal insulating diamond, secondary nucleation and microtwinning phenomena occur in the epitaxial diamond film which tend to destroy the single crystal character of the epitaxial diamond film when grown on large area (for example, 1 mm.times.1 mm) single crystal bulk diamond substrates. This secondary nucleation and microtwin crystal formation during diamond film growth is discussed by Spitsyn, et al, Journal of Crystal Growth, Vol. 52, page 219 (1981).
As a result of the foregoing problems and deficencies, it has not been possible to fabricate semiconductor devices which comprise large area epitaxially grown, single crystal semiconducting diamond films, or large area epitaxially grown, single crystal semiconducting films of the other crystalline materials illustratively referred to hereinabove. This fact has greatly restricted the application of these otherwise highly desirable crystalline materials in the manufacture of high performance electronic devices.
These drawbacks are overcome in accordance with the present invention, by the provision of textured substrates, epitaxial single crystal substrate articles, semiconducting devices, and associated manufacturing methods, as described hereinafter in detail.